Understanding the mechanism of control of energy metabolism is central to understanding cellular homeostasis. Defects in energy metabolism are associated with a number of disease states. In order to study this problem, we are developing NMR and transgenic mouse techniques. The use of molecular genetics to engineer cells to aid in the investigation of energy metabolism represents a powerful addition to the growing arsenal of techniques which can be used study cellular metabolism in vivo. In particular, alteration of creatine kinase levels and isoenzyme distribution is leading to information about the regulation of mitochondrial energy metabolism and potential new avenues for engineering cellc for medical applications. The major objective of this project is to conbine NMR and transgenic mice technology to study cellular enegy metabolism in the liver, muscle, heart, and brain. Previously, we reported the use of transgenic mouse techniques to express the brain (BB) isoenzyme of creatine kinase in the liver, to alter creatine kinase isoenzyme in muscle, and to express mitochondrial CK in liver. In the past year, we have continued the analysis of these existing transgenic mice and we have begun work on producing a transgenic mouse which express myoglobin in brain. Using 31P NMR spectroscopy in a transgenic mouse model with the expression of the B isoenzyme of creatine kinase (CK), we had previously determined the free ADP concentration, assuming the equilibrium to be established with CK. For the first time, we have tested the validity of this equilibrium assumption. We have also used these mice to study the role of creatine kinase during periods of low oxygen and the role of ADP and inorganic phosphate in regulation o fhepatic oxidative metabolism.